[MM-62427] Add message attachments validation (#30180)

* Add message attachments validation

* Add props validation

* Validate slack attachment fields

* Update tests and library usage

* Improve interactive dialog error for length checks

* Allow predefined colors for slack attachments

* Fix TestPostAction

* Use const for data source

* Add tests

* Cleanup unused props

* Add happy path tests

* lint fixes

* Add validation for PostActionOptions

server/channels/store/store.go

@@ -364,7 +364,7 @@ type ThreadStore interface {
 }
 
 type PostStore interface {
-	SaveMultiple(posts []*model.Post) ([]*model.Post, int, error)
+	SaveMultiple(rctx request.CTX, posts []*model.Post) ([]*model.Post, int, error)
 	Save(rctx request.CTX, post *model.Post) (*model.Post, error)
 	Update(rctx request.CTX, newPost *model.Post, oldPost *model.Post) (*model.Post, error)
 	Get(ctx context.Context, id string, opts model.GetPostsOptions, userID string, sanitizeOptions map[string]bool) (*model.PostList, error)
@@ -394,7 +394,7 @@ type PostStore interface {
 	InvalidateLastPostTimeCache(channelID string)
 	GetPostsCreatedAt(channelID string, timestamp int64) ([]*model.Post, error)
 	Overwrite(rctx request.CTX, post *model.Post) (*model.Post, error)
-	OverwriteMultiple(posts []*model.Post) ([]*model.Post, int, error)
+	OverwriteMultiple(rctx request.CTX, posts []*model.Post) ([]*model.Post, int, error)
 	GetPostsByIds(postIds []string) ([]*model.Post, error)
 	GetEditHistoryForPost(postID string) ([]*model.Post, error)
 	GetPostsBatchForIndexing(startTime int64, startPostID string, limit int) ([]*model.PostForIndexing, error)